A microphone which has been widely used in mobile devices, acoustic devices, vehicles, or the like senses a sound, that is, a sound wave, and converts the sound into a physical value or an electrical value. The converted signal is processed to be a signal which may be captured by a person or a machine.
Since the microphone receives a natural signal such as the sound wave, analog signal processing is essentially performed for signal conversion. Performance of a circuit for processing an analog signal may directly affect the overall performance of the microphone. In particular, the microphone receives a wide frequency range of a signal due to its characteristics and therefore noise characteristics are very important.
The microphone has a thin film applied with a pressure due to the sound pressure and thus an interval between two electrodes is changed. As a result, since capacitance is changed, the microphone converts a change amount of the capacitance into a voltage output using a buffer and outputs a digital signal. The typical microphone receives a single input signal and therefore outputs power supply noise and noise included in a bias voltage through the buffer as they are, such that sensitivity of the microphone may deteriorate. As a result, a high sensitivity microphone may show inappropriate performance.
Further, a signal-to-noise ratio (SNR) of the existing microphone applied to a vehicle is not good, such that customer dissatisfaction with a speech recognition rate or handsfree performance has been raised.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.